The present invention relates to bladders used in tire building, and more particularly to shaping bladders used in conjunction with machines for building radial ply tires by the "two-stage" process or by the "single-stage" process, both known in the art.
Shaping uncured radial tire carcasses from a generally cylindrical shape to a toroidal shape during a tire building process is well known. Early efforts to do this involved the use of a simple, rubber-like cylinder, unreinforced by filamentous material, to support the carcass during shaping. This proved unsatisfactory in that inadequate support was provided to the carcass shaped thereon for the subsequent application and stitching of the breakers and tread, and symmetry of carcass stretch about the central plane of the tire perpendicular to the axis of the tire and circumferential uniformity of stretch in planes parallel to the central plane could not be assured and were seldom achieved.
Radial tires have been shaped without the use of any bladder, the logic being that since the uncured carcass was sufficiently impervious to air, it could itself be used as a shaping means by the simple expedient of sealing the tire beads to a support means and introducing air under pressure internal to the carcass. Once the carcass had been shaped, bell-shaped cylindrical supports, positioned at each bead of the carcass, would encompass the carcass at its outer diameter and provide support for the application and stitching of the breakers and tread. This method also proved unsatisfactory in that it was cumbersome, expensive, slow and produced expanded carcasses of the same unsatisfactory uniformity described above.
Some effort has been made to return to bladder shaping wherein the bladder is reinforced in order to make the bladder an effective support means. See, for example, U.S. Pat. No. 3,138,510 issued June 23, 1964. The reinforced bladder, however, has proved unsatisfactory because of the unyielding nature of the reinforcing materials used.
U.S. Pat. No. 3,144,374, issued Aug. 11, 1964, discloses "an annular membrane (shaping bladder) reinforced with longitudinal cables which are partially and elastically extensible, thus permitting, on the one hand, to impart to the membrane a cylindrical shape having sufficient rigidity for the manufacture of the carcass of the tire, when the membrane is stretched between the separated flanges of a drum, and, on the other hand, to give limited elongation to this membrane under the effect of the inflation pressure during the shaping operation, this elongation permitting the tension of the carcass of the tire to be increased". It is stated in the U.S. Pat. No. 3,144,374 that "the limited extensibility of the longitudinal cables of the membrane can be obtained, for example, by undulating the metal cables, or by using cables of synthetic wires or braids comprising a compressible or elastic central strand". It is important to note that the reinforcing longitudinal cables are utilized to provide both partial extensibility and rigidity to the membrane. The objective to be achieved by the use of the longitudinal, extensible cables is to permit sufficient outside development of the membrane in an axial direction in relation to the carcass of the tire so that the carcass is tensioned and its deformation is adequate. However, using the technique of the U.S. Pat. No. 3,144,374 it is difficult to accurately control the axial extension of the reinforcing cables. The instant invention does not rely on any cables to provide extensibility to the bladder.
It should be noted that the U.S. Pat. No. 3,144,374 uses cables to give both rigidity and a limitation of stretch, presumably distributed along the length of the cables. The instant invention, as will more fully appear below, provides stretch at convolutions determined by the geometry of the convolutions, and provides rigidity between convolutions determined by the thickness of the bladder and the modulus of reinforcement material in the bladder.